Might have to go aftermarket to get 16s, GM really didn't offer the 1/2 ton with 16s on the later trucks, then the ones that did use the wrong offset. There is one possible option, if you can come across a '88-'90ish light duty 3/4 ton 2wd. Some of those did have 6 lug wheels. They're not as common as their 4x4 kin, but they do exist. The do use the larger lug nut, that might require some searching at the flaps to get one to fit, possibly even converting to 1/2" studs to get a nut with a larger seat area.
57 vroom vroom, the thickness of spacer that would be required to make them work would also make them very dangerous, I would advise against it. You would need to change out the studs to ones at least 3-4" long to accomodate the spacer. The chance of wheel separation is greatly increased by the extra stain that the studs would be under.
